PRC is the most common malignancy in males and the second-leading cause of cancer-related death in the United States and Europe (Gronberg H. Lancet 2003; 361:859-64.), and frequency of PRC has been increasing significantly in most developed countries probably due to prevalent western-style diet and the explosion of the aging population (Gronberg H. Lancet 2003; 361:859-64., Hsing A W, Devesa S S. Epidemiol Rev 2001; 23:3-13.). Surgical and radiation therapies are effective to the localized disease, but nearly 30% of treated PRC patients still suffer from the relapse of the disease (Feldman B J, Feldman D. Nat Rev Cancer 2001; 1:34-45., Han M, et. al, J Urol 2001; 166:416-9., Isaacs W, et. al., Cancer Cell 2002; 2:113-6.). Most of the patients with relapsed or advanced disease respond well to androgen-ablation therapy because PRCs are usually androgen-dependent at a relatively early stage. However, they often acquire androgen-independent phenotype and show no or very poor response to the androgen ablation therapy. No effective anti-cancer drug or therapy is presently available to the advanced or recurrent androgen-independent PRC. Hence, development of new therapies on the basis of the molecular mechanisms of prostate carcinogenesis or hormone refractory is urgently and eagerly required.
Earlier we performed genome-wide cDNA microarray analysis of PRC cells purified from clinical cancer tissues by means of LMM (Laser Microbeam Microdissection) and identified dozens of genes whose expression levels were evidently increased in PRC cells and/or its precursor PINs, comparing with normal prostatic epithelial cells (Ashida S, et al., Cancer Res 2004; 64:5963-72.). Among the trans-activated genes, we here report characterization of a novel gene, ELOVL7 (Genebank Accession No. NM—024930, SEQ ID NO.14, encoding SEQ ID NO.15), which is very likely to play a significant role in long-chain fatty acids synthesis. ELOVL (elongation of very long chain fatty acids) family are human homologues of yeast ELOs and catalyze the elongation reaction of the long-chain fatty acids (Leonard A E, et. al., Prog Lipid Res 2004; 43: 36-54. Wang Y, et. al., J Lipid Res 2005; 46: 706-15.). The elongation system, which responsible for the addition of two carbon units to the carboxyl end of a fatty acid chain, is composed of four enzymes: a condensing enzyme (elongase, β-ketoacyl CoA synthase), β-ketoacyl CoA reductase, β-hydroxyacyl CoA dehydrase, and trans-2,3-enoyl-CoA reductase (Leonard A E, et. al., Prog Lipid Res 2004; 43: 36-54.), and the rate of fatty acid elongation is determined by the activity of the elongase (Wang Y, et. al., J Lipid Res 2005; 46: 706-15.). Six distinct fatty acid elongase subtypes (ELOVL1-6) are reported in the mammalian so far, and each of these multiple elongation enzymes is thought to work specifically for different chain length saturated or unsaturated fatty acids (Leonard A E, et. al., Prog Lipid Res 2004; 43: 36-54., Wang Y, et. al., J Lipid Res 2005; 46: 706-15. Suneja S K, et. al., Biochim Biophys Acta. 1990; 1042: 81-5.). The metabolic pathways of long-chain fatty acids plays an important role in the maintenance of membrane lipid composition and the generation of precursors for certain cell signaling molecules, such as eicosanoids (Leonard A E, et. al., Prog Lipid Res 2004; 43: 36-54., Wang Y, et. al., J Lipid Res 2005; 46: 706-15.), thus these metabolic pathways are expected to involve some essential activity of cancer cells.
cDNA microarray technologies have provided comprehensive profiles of gene expression in normal and malignant cells, and the ability to compare the gene expression in malignant and corresponding normal cells (Okabe et al., Cancer Res 61:2129-37 (2001); Kitahara et al., Cancer Res 61: 3544-9 (2001); Lin et al., Oncogene 21:4120-8 (2002); Hasegawa et al., Cancer Res 62:7012-7 (2002)). This approach enables understanding of the complex nature of cancer cells, and helps to understand the mechanism of carcinogenesis. Identification of genes that are deregulated in tumors can lead to more precise and accurate diagnosis of individual cancers, and to develop novel therapeutic targets (Bienz and Clevers, Cell 103:311-20 (2000)). To disclose mechanisms underlying tumors from a genome-wide point of view, and to discover target molecules for diagnosis and development of novel therapeutic drugs, the present inventors have been analyzing the expression profiles of tumor cells using a cDNA microarray of 23040 genes (Okabe et al., Cancer Res 61:2129-37 (2001); Kitahara et al., Cancer Res 61:3544-9 (2001); Lin et al., Oncogene 21:4120-8 (2002); Hasegawa et al., Cancer Res 62:7012-7 (2002)).
Studies designed to reveal mechanisms of carcinogenesis have already facilitated identification of molecular targets for anti-tumor agents. For example, inhibitors of farnesyltransferase (FTIs) which were originally developed to inhibit the growth-signaling pathway related to Ras, whose activation depends on posttranslational farnesylation, has been effective in treating Ras-dependent tumors in animal models (Sun J, et. al., Oncogene 16: 1467-73 (1998)). Clinical trials on human using a combination or anti-cancer drugs and anti-HER2 monoclonal antibody, trastuzumab, have been conducted to antagonize the proto-oncogene receptor HER2/neu; and have been achieving improved clinical response and overall survival of breast-cancer patients (Molina M A, et. al., Cancer Res 61:4744-4749 (2001)). A tyrosine kinase inhibitor, STI-571, which selectively inactivates bcr-abl fusion proteins, has been developed to treat chronic myelogenous leukemias wherein constitutive activation of bcr-abl tyrosine kinase plays a crucial role in the transformation of leukocytes. Agents of these kinds are designed to suppress oncogenic activity of specific gene products (O'Dwyer M E and Druker B J, Curr Opin Oncol 12:594-7 (2000)). Therefore, gene products commonly up-regulated in cancerous cells may serve as potential targets for developing novel anti-cancer agents. In fact, novel drugs targeting abnormally expressed molecules that have causative effects on cancer growth and progression have been proven to be effective to certain types of cancers. Such drugs include Herceptin for breast cancer, Glivec (STI571) for CML and Iressa (ZD1839) for non-small cell lung cancer.
Several molecules have been known to be over-expressed in PRC and are identified as therapeutic targets or markers of PRC (Xu et al., Cancer Res 60: 6568-72 (2000); Luo et al., Cancer Res 62: 2220-6 (2002)). However, most of them are also highly expressed in other major organs. Thus, agents that target these molecules may be toxic to cancer cells but may also adversely affect normally growing cells of other organs.
It has been demonstrated that CD8+ cytotoxic T lymphocytes (CTLs) recognize epitope peptides derived from tumor-associated antigens (TAAs) presented on MHC Class I molecule, and lyse tumor cells. Since the discovery of MAGE family as the first example of TAAs, many other TAAs have been discovered using immunological approaches (Boon, Int J Cancer 54: 177-80 (1993); Boon and van der Bruggen, J Exp Med 183: 725-9 (1996); van der Bruggen et al., Science 254: 1643-7 (1991); Brichard et al., J Exp Med 178: 489-95 (1993); Kawakami et al., J Exp Med 180: 347-52 (1994)). Some of the discovered TAAs are now in the stage of clinical development as targets of immunotherapy. TAAs discovered so far include MAGE (van der Bruggen et al., Science 254: 1643-7 (1991)), gp100 (Kawakami et al., J Exp Med 180: 347-52 (1994)), SART (Shichijo et al., J Exp Med 187: 277-88 (1998)), and NY-ESO-1 (Chen et al., Proc Natl Acad Sci USA 94: 1914-8 (1997)). On the other hand, gene products which had been demonstrated to be specifically over-expressed in tumor cells, have been shown to be recognized as targets inducing cellular immune responses. Such gene products include p53 (Umano et al., Brit J Cancer 84: 1052-7 (2001)), HER2/neu (Tanaka et al., Brit J Cancer 84: 94-9 (2001)), CEA (Nukaya et al., Int J Cancer 80: 92-7 (1999)), and so on.
In spite of significant progress in basic and clinical research concerning TAAs (Rosenberg et al., Nature Med 4: 321-7 (1998); Mukherji et al., Proc Natl Acad Sci USA 92: 8078-82 (1995); Hu et al., Cancer Res 56: 2479-83 (1996)), only limited number of candidate TAAs for the treatment of adenocarcinomas, including colorectal cancer, are available. TAAs abundantly expressed in cancer cells, and at the same time which expression is restricted to cancer cells would be promising candidates as immunotherapeutic targets. Further, identification of new TAAs inducing potent and specific antitumor immune responses is expected to encourage clinical use of peptide vaccination strategy in various types of cancer (Boon and van der Bruggen, J Exp Med 183: 725-9 (1996); van der Bruggen et al., Science 254: 1643-7 (1991); Brichard et al., J Exp Med 178:489-95 (1993); Kawakami et al., J Exp Med 180: 347-52 (1994); Shichijo et al., J Exp Med 187: 277-88 (1998); Chen et al., Proc Natl Acad Sci USA 94: 1914-8 (1997); Harris, J Natl Cancer Inst 88: 1442-55 (1996); Butterfield et al., Cancer Res 59: 3134-42 (1999); Vissers et al., Cancer Res 59: 5554-9 (1999); van der Burg et al., J Immunol 156: 3308-14 (1996); Tanaka et al., Cancer Res 57: 4465-8 (1997); Fujie et al., Int J Cancer 80: 169-72 (1999); Kikuchi et al., Int J Cancer 81: 459-66 (1999); Oiso et al., Int J Cancer 81: 387-94 (1999)).
It has been repeatedly reported that peptide-stimulated peripheral blood mononuclear cells (PBMCs) from certain healthy donors produce significant levels of IFN-α or γ in response to the peptide, but rarely exert cytotoxicity against tumor cells in an HLA-A24 or -A0201 restricted manner in 51Cr-release assays (Kawano et al., Cancer Res 60: 3550-8 (2000); Nishizaka et al., Cancer Res 60: 4830-7 (2000); Tamura et al., Jpn J Cancer Res 92: 762-7 (2001)). However, both of HLA-A24 and HLA-A0201 are one of the common HLA alleles in Japanese, as well as Caucasian populations (Date et al., Tissue Antigens 47: 93-101 (1996); Kondo et al., J Immunol 155: 4307-12 (1995); Kubo et al., J Immunol 152: 3913-24 (1994); Imanishi et al., Proceeding of the eleventh International Histocompatibility Workshop and Conference Oxford University Press, Oxford, 1065 (1992); Williams et al., Tissue Antigen 49: 129 (1997)). Thus, antigenic peptides of cancers presented by these HLAs may be especially useful for the treatment of cancers among Japanese and Caucasian populations. Further, it is known that the induction of low-affinity CTL in vitro usually results from the use of peptide at a high concentration, generating a high level of specific peptide/MHC complexes on antigen presenting cells (APCs), which will effectively activate these CTL (Alexander-Miller et al., Proc Natl Acad Sci USA 93: 4102-7 (1996)).